1. Technical Field
The present invention relates to technology for printing images by forming dots on a printing medium.
2. Related Art
As output devices of images created by computers or images taken by digital cameras, printing devices that print images by forming dots on printing media are widely used. Halftone processes are employed to represent tones in such printing devices, since a smaller number of tones are available for dot formation than a number of input tone values. As one of halftone processes, ordered dither methods employing dither matrices are widely used. The ordered dither methods produce significant effects on image quality depending on how contents of the dither matrices are. Therefore, there have been attempts taken to optimize the dither matrices by means of analytical methods such as simulated annealing, genetic algorithm, and the like employing evaluation functions in consideration of human visual sensitivity, as disclosed in JP-A-7-177351, for example. Meanwhile, there have also been techniques proposed to improve dispersibility of plural types of dots in a printed image that is formed by combining the plural types of dots having different densities and/or hues from each other all together as disclosed in JP-A-10-157167.
However, in such halftone processes, no consideration has been given to deterioration of image quality that may be caused by ejecting plural colors of ink droplets on a printing medium while scanning a common print area on the printing medium and thereby printing an image (color-mixed irregularity of the plural colors of inks that may occur in each main scan).